An international team of scientists from the United States and Canada has discovered the first direct evidence that aqueous pockets may exist as far as 500 miles (805 km) deep into the Earth’s mantle.
The team, led by University of Nevada, Las Vegas geoscientist Oliver Tschauner, found inclusions of the high-pressure form of water called Ice-VII in natural diamonds sourced from between 255 and 410 miles (410-660 km) depth.
“In the jewelry business, diamonds with impurities hold less value,” the researchers said.
“But for us, those impurities — known as inclusions — have infinite value, as they may hold the key to understanding the inner workings of our planet.”
For the study, Professor Tschauner and co-authors used diamonds found in the South Africa (Namaqualand), Botswana (Orapa), China (Shandong), Zaire, and Sierra Leone.
“This shows that this is a global phenomenon,” they said. “These diamonds were born in the mantle under temperatures reaching more than 1,000 degrees Fahrenheit (538 degrees Celsius).”
“The mantle, which makes up more than 80% of the Earth’s volume, is made of silicate minerals containing iron, aluminum, and calcium among others. And now we can add water to the list.”
Ice-VII, a high-pressure form of water ice that is stable above 2.4 gigapascals (24,000 atmospheres), had been found in prior lab testing of materials under intense pressure.
The scientists found that while under the confines of hardened diamonds found on the surface of the planet, Ice-VII is solid. But in the mantle, it is liquid.
“These discoveries are important in understanding that water-rich regions in the Earth’s interior can play a role in the global water budget and the movement of heat-generating radioactive elements,” Professor Tschauner said.
“They can help us create new, more accurate models of what’s going on inside the Earth, specifically how and where heat is generated under the Earth’s crust.”
“In other words: it’s another piece of the puzzle in understanding how our planet works.”
The findings are published in the journal Science.
O. Tschauner et al. 2018. Ice-VII inclusions in diamonds: Evidence for aqueous fluid in Earth’s deep mantle. Science 359 (6380): 1136-1139; doi: 10.1126/science.aao3030